Heat exchanger and refrigerant cycle device using the same

ABSTRACT

A heat exchanger usable as an evaporator in a refrigerant cycle device includes a heat exchanging portion configured to perform heat exchange between refrigerant and air so as to evaporate the refrigerant. A thermal deformation member is provided in en entire range on a surface of the heat exchanging portion, to be deformed bordering on a predetermined temperature when the surface of the heat exchanging portion is frosted to produce ice. The thermal deformation member is deformed by a temperature change between a first temperature lower than the predetermined temperature and a second temperature higher than the predetermined temperature, to cause distortion between the surface of the heat exchanging portion and the ice when the ice is attached to the surface of the heat exchanging portion. Thus, the ice attached to the surface of the heat exchanging portion can be effectively removed while heat energy for removing the ice can be reduced.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2010-032229 filed on Feb. 17, 2010, the contents of which are incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a heat exchanger usable as an evaporator, and a refrigerant cycle device using the same.

BACKGROUND OF THE INVENTION

Patent Document 1 (JP Patent No. 4269660) describes regarding the technique for easily removing frost attached to an evaporator for a refrigerant cycle device.

In the Patent Document 1, a surface portion A, in which the frosted ice is easy to be melted, and a surface portion B, which is difficult to be frosted, are arranged to be dispersed on the surface of each plate fin of the evaporator. Thus, in a defrosting operation, ice attached to the surface portion A can be easily separated from the surface portion A by melting, and thereby the ice attached to the surface portion B can be also easily separated from the surface portion B. Therefore, heat energy required in the defrosting can be made smaller.

Furthermore, in Patent Document 1, a plate movable member is provided at an upstream end portion of the plate fins in the air flow. The plate movable member is shaped along the surface of the plate fin, when the surface temperature of the plate fin is higher than a predetermined temperature. In contrast, when the surface temperature of the plate fin is lower than the predetermined temperature, a part of the plate movable member is deformed and is separated from the surface of the plate fin. Because a part of the plate movable member is deformed, cut lines can be easily formed in the ice attached to the plate fins, and the ice can be easily separated by a wind force.

In the Patent Document 1, the plate movable member is provided only in a part of the surface area of the plate fin in order to supplement the separation of the ice from the plate fin.

Furthermore, the temperature of the evaporator is increased to an ice melting temperature, and is maintained to the ice melting temperature for a predetermined time, so that the ice attached to the plate fin can be melted and separated from the plate fin to fall. In this case, the heat energy used in the defrosting cannot be effectively reduced.

SUMMARY OF THE INVENTION

The present invention is made in view of the above matters, and it is an object of the present invention to provide a heat exchanger usable as an evaporator, which can effectively reduce heat energy used in a defrosting.

It is another object of the present invention to provide a refrigerant cycle device including the heat exchanger.

According to an aspect of the present invention, a heat exchanger usable as an evaporator in a refrigerant cycle device includes a heat exchanging portion configured to perform heat exchange between refrigerant and air so as to evaporate the refrigerant, and a thermal deformation member provided in en entire range on a surface of the heat exchanging portion to be deformed bordering on a predetermined temperature when the surface of the heat exchanging portion is frosted to produce ice. Furthermore, the thermal deformation member is deformed by a temperature change between a first temperature lower than the predetermined temperature and a second temperature higher than the predetermined temperature, to cause distortion between the surface of the heat exchanging portion and the ice when the ice is attached to the surface of the heat exchanging portion. Thus, the ice attached to the surface of the heat exchanging portion can be effectively removed by using the thermal deformation member. Therefore, it is unnecessary to melt the ice for removing the ice attached to the surface of the heat exchanging portion, thereby effectively reducing heat energy used for defrosting.

For example, the predetermined temperature is lower than freezing point. In this case, the ice attached to the surface of the heat exchanging portion can be removed without melting the ice, thereby more effectively reducing heat energy used for defrosting.

The thermal deformation member may include plural thermal deformation parts which are arranged separately in dispersion in the entire range of the surface of the heat exchanging portion. In this case, a distance between adjacent thermal deformation parts at an upstream portion of an air flow may be larger than a distance between adjacent thermal deformation parts at a downstream portion of the air flow, on the surface of the heat exchanging portion. Alternatively/Further, the thermal deformation parts at an upstream portion of an air flow may be respectively larger than the thermal deformation parts at a downstream portion of the air flow, on the surface of the heat exchanging portion. Furthermore, the sizes of the thermal deformation parts may be gradually reduced from an upstream air side to a downstream air side.

Alternatively, the thermal deformation member may have an angle portion on its outer surface. Alternatively, the thermal deformation member may be made of a shape memory alloy. In this case, the thermal deformation member may include a first member having a transformation temperature, and a second member having a transformation temperature lower than that of the first member. In this case, when temperature of the thermal deformation member is increased from a temperature lower than the transformation temperature of the first member to a temperature higher than the transformation temperature of the first member, the first member becomes in a memorized shape and the second member is deformed by the memorized shape of the first member. Furthermore, when the temperature of the thermal deformation member is decreased from a temperature higher than the transformation temperature of the first member to a temperature lower than the transformation temperature, the first member is deformed by an elastic force of the second member.

The thermal deformation member may be made of an organic material or a complex material, which is deformable by a temperature change bordering on the predetermined temperature, or the thermal deformation member may be made of a bimetal.

The heat exchanging portion may include a plurality of tubes and a plurality of fins which are alternately arranged in an arrangement direction, and the thermal deformation member may be provided on at least one of the tubes and the fins.

The heat exchanger may be used for a refrigerant cycle device. For example, the refrigerant cycle device includes a compressor configured to discharge refrigerant, a refrigerant radiator in which the refrigerant discharged from the compressor radiates heat, a decompression device configured to decompress the refrigerant flowing out of the refrigerant radiator, the heat exchanger according to claim 1 adapted as an evaporator for evaporating the refrigerant flowing out of the decompression device, and a control portion configured to repeatedly change a surface temperature of the heat exchanging portion between a first temperature lower than the predetermined temperature and a second temperature higher than the predetermined temperature. In this case, the control portion may be configured to repeatedly change the surface temperature by changing a refrigerant discharge capacity of the compressor.

For example, the control portion may cause the compressor to be switched between a first operation, in which a discharge capacity of the compressor is lower than that of a normal operation, and a second operation in which the discharge capacity of the compressor is higher than the discharge capacity of the compressor in the first operation, when the surface of the heat exchanging portion of the evaporator is frosted in the normal operation.

The refrigerant cycle device may be provided with a bypass passage through which a part of high-temperature refrigerant higher than the refrigerant flowing into the evaporator is introduced to the evaporator, and a switching portion configured to open or close the bypass passage. In this case, the control portion repeats the opening and closing of the switching portion so as to repeatedly change the surface temperature of the heat exchanging portion, when the surface of the heat exchanging portion is frosted.

Furthermore, the bypass passage may be configured such that a part of the refrigerant after flowing through the evaporator and before flowing into a refrigerant suction side of the compressor is introduced to a refrigerant inlet side of the evaporator.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention will become more apparent from the following description made with reference to the accompanying drawings, in which like parts are designated by like reference numbers and in which:

FIG. 1 is a schematic diagram showing a refrigerant cycle device adapted to a vehicle air conditioner, according to a first embodiment of the invention;

FIG. 2 is an enlarged view showing a part of a heat exchanging portion of an exterior heat exchanger of the refrigerant cycle device of FIG. 1;

FIG. 3A is a perspective view showing a surface of a fin in an area A1 of FIG. 2 at a low temperature lower than a predetermined temperature (material deformation temperature), and FIG. 3B is a perspective view showing the surface of the fin in the area A1 of FIG. 2 at a high temperature higher than the predetermined temperature;

FIG. 4A is a partially sectional view showing the fin in the area A1 of FIG. 2 at the low temperature lower than the predetermined temperature, and FIG. 4B is a partially sectional view showing the fin in the area A1 of FIG. 2 at the high temperature higher than the predetermined temperature;

FIGS. 5A, 5B and 5C are schematically sectional views showing a thermal deformation member on the fin, according to the first embodiment;

FIG. 6 is a time chard showing a change of a surface temperature of the fin in the external heat exchanger of the first embodiment, in accordance with an operation time;

FIG. 7 is a time chard showing a change of a surface temperature of a fin in an external heat exchanger of a comparison example, in accordance with an operation time;

FIG. 8 is a schematic perspective view showing a thermal deformation member on a surface of a fin used for an evaporator, according to a second embodiment of the present invention;

FIGS. 9A and 9B are schematically sectional views showing a thermal deformation member on a fin used for an evaporator, according to a third embodiment of the present invention;

FIG. 10, is a schematically sectional view showing a thermal deformation member on a fin used for an evaporator, according to a fourth embodiment of the present invention; and

FIG. 11 is a schematic diagram showing a refrigerant cycle device according to the other embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereafter referring to drawings. In the embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned with the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination.

First Embodiment

FIG. 1 is a schematic diagram showing a refrigerant cycle device according to a first embodiment of the invention. In the present embodiment, the refrigerant cycle device is typically used for a vehicle air conditioner 1 mounted to an electrical vehicle (EV) or a hybrid vehicle (HV), for example.

As shown in FIG. 1, the air conditioner 1 includes a vapor-compression refrigerant cycle 10 and an interior air conditioning unit 20. The refrigerant cycle 10 is configured to be switchable between a cooling operation mode and a heating operation mode.

The refrigerant cycle 10 includes a compressor 11, an interior heat exchanger 12, an exterior heat exchanger 13, a decompression device 14, a four-way valve 15 and a controller (ECU) 16.

The compressor 11 is disposed in an engine compartment to draw refrigerant, to compress the drawn refrigerant and to discharge the compressed refrigerant. For example, the compressor 11 is an electrical compressor in which a fixed-displacement compression mechanism with a fixed discharge capacity is driven by an electrical motor. A rotation speed of the electrical motor is controlled by a control signal output from the controller 16, so that the refrigerant discharge capacity of the compressor 11 is changed by the rotation speed control. Therefore, the electrical motor is adapted as a discharge capacity changing portion of the compressor 11 in the present embodiment.

The interior heat exchanger 12 is disposed to perform heat exchange between the refrigerant and air to be blown into a vehicle compartment.

The exterior heat exchanger 13 is disposed to perform heat exchange between the refrigerant and outside air outside of the vehicle compartment. The decompression device 14 is configured to decompress and expand the refrigerant.

The four-way valve 15 is adapted as a flow switching portion, to switch the refrigerant flow in the refrigerant cycle 10 between the cooling operation mode and the heating operation mode. The four-way valve 15 is connected to a refrigerant discharge side of the compressor 11 to switch the refrigerant flow of the refrigerant cycle 10 based on a control signal output from the controller 16.

Specifically, in the cooling operation mode, the refrigerant is circulated as in the solid line arrows of FIG. 1, in this order of the compressor 11, the exterior heat exchanger 13, the decompression device 14, the interior heat exchanger 12 and the compressor 11. Thus, the refrigerant discharged from the compressor 11 is heat-radiated to the outside in the exterior heat exchanger 13, is decompressed in the decompression device 14, and absorbs heat from air to be blown into the vehicle compartment in the interior heat exchanger 12. Therefore, the exterior heat exchanger 13 is used as a refrigerant radiator, and the interior heat exchanger 12 is used as a refrigerant evaporator, in the cooling operation mode. Accordingly, in the cooling operation mode, air blown into the vehicle compartment is cooled by the interior heat exchanger 12.

In the heating operation mode, the refrigerant is circulated as in the chain line arrows of FIG. 1, in this order of the compressor 11, the interior heat exchanger 12, the decompression device 14, the exterior heat exchanger 13 and the compressor 11. Thus, the refrigerant discharged from the compressor 11 radiates heat to air in the interior heat exchanger 12, is decompressed and expanded in the decompression device 14, and absorbs heat from outside air in the exterior heat exchanger 13. Therefore, the exterior heat exchanger 13 is used as a refrigerant evaporator, and the interior heat exchanger 12 is used as a refrigerant radiator, in the heating operation mode. Accordingly, in the cooling operation mode, air blown into the vehicle compartment is heated by the interior heat exchanger 12.

The interior air-conditioning unit 20 includes an air conditioning case 21 defining an air passage through which air flows into the vehicle compartment. A blower 22 for, generating an air flow in the air conditioning case 21 and the interior heat exchanger 12 are disposed in the air conditioning case 21.

The controller 16 can be used as an air conditioning controller for controlling air conditioning operation. The controller 16 includes a microcomputer configured by CPU, ROM, RAM, etc., and a circumference circuit. Calculations and processes are performed based on air-conditioning control program stored in the ROM. The controller 16 controls operation of various components such as the compressor 11, the four-way valve 15, the blower 22, an exterior blower 13 a and the like, based on operation signals input from an operation panel and sensor signals input from a sensor group. The sensor signals include signals indicating vehicle environment states. Thus, the refrigerant cycle 10 can be operated selectively as the heating operation mode or the cooling operation mode, and the compressor 11 can be operated by a predetermined rotation speed, based on control signals.

The controller 16 may include a temperature control portion which can repeatedly change a surface temperature of a heat exchanging portion of the exterior heat exchanger 13 to be higher than a predetermined temperature and to be lower than the predetermined temperature. Furthermore, the controller 16 may include a discharge capacity control portion for controlling the discharge capacity of the refrigerant discharged from the compressor 11. Alternatively; the discharge capacity control portion of the compressor 11 may be provided separately from the controller 16. Furthermore, the various components may be respectively separately controlled by using different control portions.

FIG. 2 is an enlarged view showing a part of the heat exchanging portion of the exterior heat exchanger 13 of the refrigerant cycle device. As shown in FIG. 2, the exterior heat exchanger 13 includes a plurality of tubes 31 and a plurality of fins 32, which are alternately stacked in a stack direction (arrangement direction) to configure the heat exchanging portion. FIG. 2 shows a part of the heat exchanging portion (core portion) of the exterior heat exchanger 13.

The tubes 31 extend in a tube longitudinal direction to respectively define therein refrigerant passages. Two longitudinal end sides of the tubes 31 are connected to a pair of header tanks to communicate with the header tanks. Thus, refrigerant is distributed from one header tank into plural tubes 31, and the refrigerant after passing through the tubes 31 is joined into the other header tank.

The fin 32 is bonded to outer surfaces of adjacent tubes 31 so as to facilitate heat exchange between the refrigerant flowing inside of the tubes 31 and air flowing outside of the tubes 31. In the present embodiment, the fin 32 is a corrugated fin bent in a wave shape.

FIG. 3A is a perspective view showing a surface of the fin 32 in an area A1 of FIG. 2 at a low temperature lower than a predetermined temperature, and FIG. 3B is a perspective view showing the surface of the fin 32 in the area A1 of FIG. 2 at a high temperature higher than the predetermined temperature. FIG. 4A is a partially sectional view showing the fin 32 in the area A1 of FIG. 2 at the low temperature lower than the predetermined temperature, and FIG. 4B is a partially sectional view showing the fin 32 in the area A1 of FIG. 2 at the high temperature higher than the predetermined temperature.

As shown in FIGS. 3A and 3B, a plurality of thermal deformation members 40 (thermal deformation portions) are arranged separately in dispersion in an entire range on a surface of the fin 32. The thermal deformation member 40 is made of a material that is deformed by a temperature change bordering on a predetermined temperature (e.g., material deformation temperature). That is, the thermal deformation member 40 is deformed, when the temperature of the thermal deformation member 40 is changed from a temperature lower than the material deformation temperature to a temperature higher than the material deformation temperature, or is changed from a temperature higher than the material deformation temperature to a temperature lower than the material deformation temperature. In the examples of FIGS. 3A and 3B, all the thermal deformation members 40 have approximately the same size, and are arranged at an equal distance in the entire area of the fin. However, the plural deformation members 40 may have different shapes, or/and may be arranged in dispersion at unequal distances in the entire area of the surface of the fin 32.

More specifically, in a low surface temperature lower than the material deformation temperature, the thermal deformation member 40 has a flat shape along the surface of the fin 32, as shown in FIGS. 3A and 4A. In contrast, in a high surface temperature higher than the material deformation temperature, the thermal deformation member 40 has an expanded shape expanded from the surface of the fin 32 to a direction perpendicular to the surface of the fin 32. Thus, the thermal deformation member 40 is deformed between an expanded state and a constricted state in the direction perpendicular to the surface of the fin 32, in accordance with the temperature change between a first temperature lower than the material deformation temperature and a second temperature higher than the material deformation temperature.

The thermal deformation member 40 is deformed between the shape shown in FIG. 4A and the shape shown in FIG. 4B. Thus, if ice 50 is attached on the surface of the fin 32, the interface between the surface of the fin 32 and the ice 50, that is, the joining surface between the surface of the fin 32 and the ice 52 is distorted, and thereby the ice 50 can be separated from the surface of the fin 32.

The thermal deformation member 40 will be described in detail. FIGS. 5A, 5B and 5C are enlarged schematic views showing the thermal deformation member 40. FIG. 5A shows the thermal deformation member 40 when a surface temperature T of the fin 32 is higher than −5° C. (T>−5° C.), and FIG. 5B shows the thermal deformation member 40 when the surface temperature T of the fin 32 is in a range of −30° C.<T<−5° C. Furthermore, FIG. 5C shows the thermal deformation member 40 when the surface temperature T of the fin 32 is changed from a temperature lower than −5° C. to a temperature higher than −5° C.

The thermal deformation member 40 is made of a two-kind shape memory alloy having two different transformation temperatures. Specifically, as shown in FIG. 5A, the thermal deformation member 40 includes a first member 41 and a second member 42 which are made of shape memory alloys different from each other. The transformation temperature of the first member 41 is lower than the freezing point, and is higher than a refrigerant temperature at which frost may be caused on the exterior heat exchanger 13. On the other hand, the transformation temperature of the second member 42 is lower than the transformation temperature of the first member 41, and is lower than the refrigerant temperature at which frost is caused on the exterior heat exchanger 13. As an example, the transformation temperature of the first member 41 is −5° C., and the transformation temperature of the second member 42 is −30° C.

When the temperature of the shape memory alloy is changed bordering on the transformation temperature between a first temperature higher than the transformation temperature and a second temperature lower than the transformation temperature, the crystal structure is changed between an austenite phase and a martensite phase. When the temperature of the shape memory alloy is in a high temperature range higher than the transformation temperature of the shape memory alloy, the shape memory alloy becomes in the austenite phase. In contrast, when the temperature of the shape memory alloy is in a low temperature range lower than the transformation temperature of the shape memory alloy, the shape memory alloy becomes in the martensite phase. The shape memory alloy has elasticity in austenite phase; however, the shape memory alloy loses the elasticity in martensitic phase. For this reason, in a temperature range higher than the transformation temperature of the shape memory alloy, an elastic force is effective to work to the external force, and it will be difficult to be deformed by external force, and thereby the memorized shape of the shape memory alloy is maintained. However, in a temperature range lower than the transformation temperature of the shape memory alloy, the shape memory alloy will be easily deformed by an external force.

As the shape memory alloy, a generally known alloy such as Ni—Ti alloy and a Cu—Zn—Al alloy or the like may be used, for example. Because the transformation temperature of the shape memory alloy is determined by alloy composition, a processing method, a heat treatment condition, etc., the shape memory alloy may be suitably selected based on a necessary transformation temperature. In addition, it is desirable that hysteresis range is small in the shape memory alloy, because the deformation of the shape memory alloy can be performed in a small temperature change range as the hysteresis range is smaller.

In the example of FIGS. 5A, 5B and 5C of the present embodiment, in a first temperature range higher than the transformation temperature (e.g., −5° C.) of the first member 41, the first member 41 becomes in a corrugated plate shape bent in a wave shape. In contrast, in a second temperature range lower than the transformation temperature (e.g., −5° C.) of the first member 41 and higher than the transformation temperature (e.g., −30° C.) of the second member 42, the second member 41 becomes in a flat plate shape along the surface of the fin 32. Furthermore, in a temperature range higher than the transformation temperatures of both the first member 41 and the second member 42, the force of the first member 41 for maintaining the shape of the first member 41 is stronger than the force of the second member 42 for maintaining the shape of the second member 42.

When the surface temperature of the fin 32 is higher than −5° C., the surface temperature is higher than the transformation temperatures of both the first member 41 and the second member 42. In this case, as shown in FIG. 5A, the first member 41 becomes in the austenite phase, and keeps the corrugated plate shape as the memorized shape. Thus, the second member 42 is elastically deformed by the elastic force of the first member 41, and is bent in a wave shape, as shown in FIG. 5B. At this time, a force for changing the shape of the second member 42 from the deformed bent shape to the memorized, flat shape is applied to the first member 41.

When the fin 32 is cooled and the surface temperature T is decreased to a temperature in the range of −5° C. and −30° C., the surface temperature T becomes lower than the transformation temperature of the first member 41. In this case, the first member 41 is changed to the martensite phase, and is easy to be deformed by the external force, and the second member 42 becomes in the memorized flat shape as shown in FIG. 5B. By the elastic force of the second member 42, the first member 41 is enlarged and extended in a direction parallel with the surface of the fin 32, and is deformed from the state of FIG. 5A to the state of FIG. 5B. As a result, when the surface temperature T becomes in the range of −5° C. and −30° C. from a temperature higher than −5° C., the thermal deformation member 40 totally extends in the direction parallel to the surface of the fin 32, and is constricted in the direction perpendicular to the surface of the fin 32.

When the surface temperature T of the fin 32 is increased from the state of FIG. 5B to a temperature higher than −5° C., the surface temperature T of the fin 32 becomes higher than the transformation temperature of the first member 41, and thereby the first member 41 becomes in the austenite phase. Therefore, as shown in FIG. 5C, the first member 41 is changed to the corrugated plate shape that is the memorized shape of the first member 41. As a result, the entire of the thermal deformation member 40 is constricted in the direction parallel to the surface of the fin 32, and is expanded in the direction perpendicular to the surface of the fin 32.

In the present embodiment, the transformation temperature of the first member 41 is the material deformation temperature of the thermal deformation member 40. When the surface temperature T of the fin 32 is changed in a temperature range over the deformation temperature of the first member 41, the dimension of the thermal deformation member 40 is changed in the direction perpendicular to the surface of the fin 32, and the thermal deformation member 40 is expanded or constricted in the direction perpendicular to the surface of the fin 32.

The first member 41 and the second member 42 are fixed at contact portions therebetween, and the second member 42 is fixed to the surface of the fin 32 at a center portion 42 a of the second member 42. The center portion 42 a of the second member 42 is configured, such that the flat shape of the center portion 42 a of the second member 42 can be maintained even when the surface temperature of the fin 32 is changed in the temperature range over the transformation temperature. Thus, the center portion 42 a of the second member 42 can be effectively fixed to the surface of the fin 32. In the present embodiment, the center portion 42 a of the second member 42 is fixed to the surface of the fin 32. However, the other portion of the second member 42 except for the center portion may be fixed to the surface of the fin 32. That is, a part of the second member 42 may be fixed to the surface of the fin 32 by using a flat portion of the second member 42.

Next, air conditioning control performed by the controller 16 will be described.

In a heating operation for heating the vehicle compartment, the controller 16 causes the refrigerant cycle 10 to be operated in the heating operation mode. When condensed water is frozen and the exterior heat exchanger 13 adapted as an evaporator in the heating operation mode is frosted, the controller 16 causes the refrigerant cycle 10 to be switched from a normal operation to a defrosting operation in the heating operation mode. Then, when the defrosting operation of the exterior heat exchanger 13 is finished, the controller 16 causes the refrigerant cycle 10 to be returned to the normal operation in the heating operation mode.

In the normal operation of the heating operation mode, the refrigerant cycle 10 is operated based on air-conditioning load (e.g., necessary heating capacity), and the controller 16 determines a control target value based on operation signals input from the operation panel and sensor signals input from the sensor group. Then, the controller 16 controls various components such as the compressor 11, in accordance with the control target value.

In the normal operation of the heating operation mode, the controller 16 determines whether frost is generated on the exterior heat exchanger 13. In the present embodiment, a refrigerant temperature sensor may be provided to detect the temperature of the refrigerant flowing out of a refrigerant outlet of the exterior heat exchanger 13. In this case, when the detected refrigerant temperature at the refrigerant outlet of the exterior heat exchanger 13 is lower than a frost determination temperature for a time longer than a predetermined time period, it is determined that the exterior heat exchanger 13 is frosted. For example, in a case where the frost determination temperature is set at −10° C., when a predetermined time has been passed for which the detected refrigerant temperature is equal to or lower than a predetermined time, the controller 16 determines that the frost of the exterior heat exchanger 13 is caused. In this case, the defrosting operation is performed in the heating operation mode.

In the defrosting operation, the frost (ice) attached to the heat exchanging portion of the exterior heat exchanger 13 is removed.

Next, the defrosting operation of the present embodiment will be described with reference to FIG. 6. FIG. 6 is a time chard showing a change of a surface temperature T of the fin 32, in accordance with an operation time. In the defrosting operation of the heating operation mode, the surface temperature T of the fin 32 is changed repeatedly between a first temperature T1 lower than a material deformation temperature Tc and a second temperature T2 higher than the material deformation temperature Tc, as shown in FIG. 6. Here, the second temperature T2 is set lower than the freezing temperature (0° C.). In the example of FIG. 6, the material deformation temperature Tc of the thermal deformation member 40 is higher than the first temperature T1 that is the surface temperature in the frosting. In the defrosting operation, the surface temperature T of the fin 32 is increased from the first temperature T1 lower than the material deformation temperature Tc to the second temperature T2 higher than the material deformation temperature Tc, and the surface temperature T of the fin 32 is maintained at the second temperature T2 for a predetermined time. Thereafter, the surface temperature T of the fin 32 is decreased from the second temperature T2 to the first temperature T1, and the surface temperature T of the fin 32 is maintained at the first temperature t1 for a predetermined time. The temperature change of the surface temperature T of the fin 32 between the first temperature T1 and the second temperature T2 is repeated. As described above, the surface temperature T of the fin 32 is repeatedly changed in the temperature range between the first temperature T1 and the second temperature T2 around the material deformation temperature Tc. For example, the material deformation temperature Tc is the transformation temperature (−5° C.) of the first member 41, the first temperature T1 is −10° C., and the second temperature T2 is −3° C.

In the present embodiment, in order to perform a temperature control in the defrosting operation, the refrigerant discharge capacity of the compressor 11 can be changed by the controller 16, while the refrigerant cycle 10 is operated also in the heating operation mode. For example, the controller 16 causes the refrigerant cycle 10 to be repeatedly switched between a first operation in which the refrigerant discharge capacity of the compressor 11 is lower than that in the normal operation, and a second operation in which the refrigerant discharge capacity of the compressor 11 is equal to that in the normal operation, thereby performing the temperature control.

When the defrosting operation is switched from the normal operation in the heating operation mode, the compressor 11 performs the first operation, such that the rotation speed of the compressor 11 is set lower than a target rotation speed of the normal operation in the heating operation mode. In the first operation, the rotation speed of the compressor 11 is set such that the detected refrigerant temperature at the refrigerant outlet of the exterior heat exchanger 13 is increased to the second temperature (e.g., −3° C.). Thus, the surface temperature T of the fin 32 is changed from the first temperature T1 (e.g., −10° C.) to the second temperature T2 (e.g., −3° C.), similarly to the refrigerant temperature change.

After the first operation of the compressor 11 is performed for a predetermined time, the controller 16 changes the rotation speed of the compressor 11 to a target rotation speed in the normal operation, so that the second operation is performed in the compressor 11. Thus, the surface temperature T of the fin 32 is changed from the first temperature T1 (e.g., −10° C.) to the second temperature T2 (e.g., −3° C.), similarly to the refrigerant temperature change.

In addition, the operation times of the first operation and the second operation are set so that the thermal deformation member 40 can be effectively deformable. Furthermore, the operation times of the first operation and the second operation are set by considering the thermal hysteresis width. The number of the temperature change in the defrosting operation can be suitably set so that the separation of the ice from the surface of the fin 32 can be performed.

Thus, when the controller 16 performs the defrosting operation of the exterior heat exchanger 12, the surface temperature of the fin 32 will change repeatedly between −10° C. and −3° C. ranging over −5° C. that is the transformation temperature of the first member 41. Thus, the thermal deformation member 40 is deformed repeatedly between the expanded state and the constricted state in the direction perpendicular to the surface of the fin 32, in accordance with the temperature change lower than or higher than the material deformation temperature, as shown in FIGS. 5A, 5B and 5C.

Thus, distortion is formed between the ice 50 attached to the surface of the fin 32, and the surface of the fin 32, the ice 50 is cracked, and thereby the ice 50 is separated from the surface of the fin 32 because a crack progresses little by little. Therefore, the ice 50 attached to the surface of the fin 32 can be removed without melting the ice.

The operation effects of the first embodiment will be described.

(1) In the exterior heat exchanger 13 adapted as the evaporator in the heating operation mode, plural thermal deformation members 40 are arranged in dispersion in the entire range of the surface of the fin 32. Furthermore, the thermal deformation members 40 are deformed in a temperature change bordering on the material deformation temperature.

Thus, in a case where the ice is attached to the surface of the fin 32, by changing the surface temperature T of the fin 32 in a temperature range over the material deformation temperature, distortion is formed between the ice and the surface of the fin 32, and thereby the ice can be separated from the surface of the fin 32. Thus, in the present embodiment, the ice attached to the surface of the fin 32 can be removed in the ice state without melting the ice. Thus, heat energy used for the defrosting of the exterior heat exchanger 32 can be effectively reduced.

(2) The material deformation temperature of the thermal deformation member 40 is set at the transformation temperature (−5° C.) of the first member 41, which is lower than the freezing point.

As shown in FIG. 6, in the defrosting operation, the surface temperature of the fin 32 is increased from the first temperature T1 (e.g., −10° C.) to the second temperature T2 (e.g., −3° C.), so that the thermal deformation member 40 is deformed. Furthermore, the second temperature T2 is set to be higher than the material deformation temperature Tc by several degree (° C.), and to be lower than the freezing point.

FIG. 7 is a time chard showing a change of a surface temperature of a fin in an external heat exchanger of a comparison example, in a defrosting operation. In the comparison example, in the defrosting operation, the ice is removed by melting. In the comparison example, a cooling operation mode is set in the refrigerant cycle in the defrosting operation, so that high-temperature refrigerant discharged from the compressor 11 flows into the exterior heat exchanger. Thus, as shown in FIG. 7, in the defrosting operation, the temperature of the exterior heat exchanger is increased to a high temperature higher than 0° C., and the high temperature is kept so that the ice is melted. Therefore, the heat energy used in the defrosting of the exterior heat exchanger is made larger.

In contrast, according to the present embodiment, the surface temperature of the fin 32 is increased to be higher than the material deformation temperature Tc by several degree (° C.), and it is unnecessary to increase the surface temperature of the fin 32 to be higher than the freezing point. Thus, the heat energy used for the defrosting can be effectively reduced as compared with the comparison example.

(3) When the surface of the fin 32 is frosted in the normal operation of the heating operation mode, the controller 16 causes the refrigerant cycle 10 to be switched from the normal operation to the defrosting operation, in the heating operation mode. That is, in the defrosting operation, the controller 16 switches the compressor 11 to be operated between the first operation and the second operation. In the first operation, the rotation speed of the compressor 11 is lower than the target rotation speed of the normal operation. In the second operation, the rotation speed of the compressor 11 is equal to the target rotation speed of the compressor 11 in the normal operation. Alternatively, in the second operation, the rotation speed of the compressor 11 may be set higher than that in the first operation, without being limited to be equal to the target rotation speed of the compressor 11 in the normal operation.

In the present embodiment, the defrosting operation is performed in the heating operation mode, and the refrigerant temperature in the exterior heat exchanger 13 is increased to perform the defrosting. Thus, even in the defrosting operation, the refrigerant cycle operation in the heating operation mode can be continuously performed.

(4) The controller 16 causes the operation of the compressor 11 to be repeatedly switched between the first operation and the second operation in the defrosting operation, so that the surface temperature of the fin 32 is repeatedly changed to be higher than the material deformation temperature Tc and to be lower than the material deformation temperature Tc.

It is difficult for the thermal deformation member 40 to be deformed by one time thermal variation straddling the material deformation temperature Tc, because the deformation of the thermal deformation member 40 is restricted by the ice. At this time, it may be impossible to generate crack between the ice and the surface of the fin 32.

In the present embodiment, because the thermal deformation member 40 can be repeatedly deformed by plural temperature changes, distortion can be easily caused between the ice and the surface of the fin 32, and thereby the crack can be caused. Therefore, the ice can be removed certainly.

(5) As shown in FIGS. 5A-5C, the thermal deformation member 40 is bent two or more times so that a mountain and a valley are alternately located, and thereby an angle portion 40 a is formed. Thus, the ice attached to the surface of the fin 32 can be easily divided by the angle portion 40 a while the thermal deformation member 40 is deformed.

Second Embodiment

A second embodiment of the present invention will be described with reference to FIG. 8. FIG. 8 is a schematic perspective view showing thermal deformation members 40 on a surface of a fin 32 used for an evaporator, according to the second embodiment.

In the second embodiment, as shown in FIG. 8, plural thermal deformation members 40 are arranged in dispersion in the entire range of the surface of the fin 32, to be separated, from each other. Furthermore, a distance L1 between adjacent thermal deformation members 40 at an upstream air side is made larger than a distance L2 between adjacent thermal deformation members 40 at a downstream air side, as shown in FIG. 8.

In addition, the size of the thermal deformation member 40 located at an upstream air side is made larger than the size of the thermal deformation member 40 located at a downstream air side. The sizes of the thermal deformation members 40 arranged in the air flow direction may be set gradually smaller along the air flow direction. Here, the size of the thermal deformation member 40 is the area of the thermal deformation member 40, occupying the surface of the fin 32.

According to the second embodiment, when the thermal deformation member 40 is deformed, the ice 50 separated from the surface of the fin 32 becomes a large-size ice piece 50 at the upstream air side, and becomes a small-size ice piece at the downstream air side, as shown in FIG. 8.

As the size of the ice piece 50 is larger, the surface area receiving the air pressure becomes larger, and thereby the force for separating the ice from the surface of the fin 32 becomes larger. Therefore, the ice piece 50 positioned at the upstream air side can be easily separated from the surface of the fin 32. When the large-size ice piece 50 positioned at the upstream air side is separated from the surface of the fin 32 and moves downstream in the air flow direction by the air pressure, the small-size ice piece 50 located at a downstream air side can be also removed by the movement of the large-size ice piece 50.

In the second embodiment, the distance L1 between the thermal deformation members 40 at the upstream air side is made larger than the distance L2 between the thermal deformation members 40 at the downstream air side, while the size of the thermal deformation member 40 at an upstream air side is made larger than the size of the thermal deformation member 40 at a downstream air side. However, the distance L1 between the thermal deformation members 40 at the upstream air side may be made larger than the distance L2 between the thermal deformation member 40 at the downstream air side, while the size of the thermal deformation member 40 at an upstream air side is approximately equal to the size of the thermal deformation member 40 at a downstream air side. Alternatively, the distance between the thermal deformation members 40 at the upstream air side may be approximately equal to the distance between the thermal deformation member 40 at the downstream air side, while the size of the thermal deformation member 40 at an upstream air side is made larger than the size of the thermal deformation member 40 at a downstream air side. In the second embodiment, the other parts may be similar to those of the above-described first embodiment.

Third Embodiment

A third embodiment of the present invention will be described with reference to FIGS. 9A and 9B. FIGS. 9A and 9B are schematically sectional views showing thermal deformation members 40 on the surface of the fin 32 used for an evaporator, according to the third embodiment.

In the present embodiment, the thermal deformation member 40 is made of a bimetal 43. This bimetal 43 is formed by bonding two-kind metal materials 43 a, 43 b having different thermal expansion coefficients. The thermal deformation members 40 configured by the bimetal 43 are disposed on the surface of the fin 32, such that the metal material 43 a with a low thermal expansion coefficient is positioned outside of the bimetal 43, and the metal material 43 b with a high thermal expansion coefficient is positioned to contact the surface of the fin 32.

Thus, in the temperature range where the surface temperature of the fin 32 is lower than material deformation temperature, the bimetal 43 becomes in a flat shape along the surface of the fin 32, as shown in FIG. 9A. In contrast, in the temperature range where the surface temperature of the fin 32 is higher than material deformation temperature, the bimetal 43 becomes in a shape bent to a side separating from the surface of the fin 32, as shown in FIG. 9B.

As the bimetal 43, a generally known bimetal may be used, if the bimetal is deformed as shown in FIG. 9A and FIG. 9B in a temperature change range of −20° C.-0° C. below the freezing point. Even in the third embodiment, the arrangement of the thermal deformation members 40 described in the above second embodiment of FIG. 8 may be adapted. In the third embodiment, the other parts may be similar to those of the above-described first embodiment.

Fourth Embodiment

A fourth embodiment of the present invention will be described with reference to FIG. 10. In the fourth embodiment, the thermal deformation member 40 is made of an organic material that is deformed by a temperature change bordering on a predetermined temperature (e.g., material deformation temperature).

As the organic material, a thermostat chromic material may be used, for example. The thermostat chromic material is an organic material, in which its color changes because molecular structure changes bordering on a predetermined temperature. Furthermore, the deformation of the thermostat chromic material is also caused because the molecular structure of the thermostat chromic material changes.

In the present embodiment, a deformation member may be formed on the surface of a heat exchanging portion of an evaporator, by applying the organic material to the surface of a fin 32 or a tube of the heat exchanging portion of a heat exchanger used as an evaporator.

In addition, as the thermal deformation member 40, instead of the above-described organic material, a complex material, in which its molecular structure changes bordering on a predetermined temperature, may be used.

Even when the thermal deformation member 40 is made of an organic material or a complex material, the thermal deformation member 40 may be formed into a shape having an angle portion 40 a, as shown in FIG. 10. When the angle portion 40 a is provided in the thermal deformation member 40, the ice crack can be easily performed. Even in the fourth embodiment, the arrangement of the thermal deformation members 40 described in the above second embodiment of FIG. 8 may be adapted. In the fourth embodiment, the other parts may be similar, to those of the above-described first embodiment.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

(1) For example, in the above-described first embodiment, the material deformation temperature Tc (e.g., −5° C.) of the thermal deformation member 40 is used as a predetermined temperature as the boundary of the temperature change of the surface temperature of the heat exchanging portion. However, other temperature may be used as the predetermined temperature.

Preferably, the material deformation temperature Tc is set to be higher than the lowest temperature (e.g., −20° C.) of the refrigerant in the normal operation of the heating operation mode, and is lower than the freezing point. By using the material deformation temperature Tc lower than the freezing point, the surface temperature of the heat exchanging portion can be changed in a temperature range below the freezing point in the defrosting operation, and thereby heat energy used for defrosting can be effectively reduced.

In addition, it is more desirable that the material deformation temperature Tc is near the frost formation temperature. In this case, the thermal deformation member 40 is deformable with respect to the surface of the heat exchanging portion, by slightly changing the surface temperature of the heat exchanging portion in the defrosting operation.

However, the thermal deformation member 40 may be made of a material having the material deformation temperature Tc higher than 0° C. In this case, the temperature of the exterior heat exchanger 13 is increased to a temperature higher than the freezing point; however, it is unnecessary to keep the temperature until the ice is melted. Thus, it is possible for the temperature of the exterior heat exchanger 13 to be decreased for a short time after the temperature is increased. Accordingly, as compared with the comparison case where the high temperature higher than the freezing point is maintained until the ice is melted, the heat energy used for the defrosting operation can be effectively reduced.

(2) In the above-described first embodiment, in the defrosting operation, the operation of the compressor 11 is switched to the first operation so that the surface temperature of the exterior heat exchanger 13 is increased more than that in the normal operation of the heating operation mode. However, conversely, in the defrosting operation, the surface temperature of the exterior heat exchanger 13 may be decreased more than that in the normal operation of the heating operation mode.

For example, when the performance required in the refrigerant cycle in the heating operation mode is small and the refrigerant temperature flowing into the exterior heat exchanger 13 is relatively high in the defrosting operation, the performance of the refrigerant cycle is increased so that the refrigerant temperature flowing into the exterior heat exchanger 13 can be reduced.

The thermal deformation member 40 may be made of a material in which the material deformation temperature Tc is lower than the surface temperature T1. In this case, the rotation speed of the compressor 11 may be increased, so as to increase the refrigerant discharge capacity and to set the refrigerant temperature flowing into the exterior heat exchanger 13 to be lower that the material deformation temperature Tc, when the frost is caused. Then, after the refrigerant temperature is decreased, the rotation speed of the compressor 11 is switched to be reduced, so that the refrigerant temperature flowing into the exterior heat exchanger 13 is increased to be higher than the material deformation temperature Tc.

(3) In the above-described first to third embodiments, the thermal deformation member 40 is provided on the surface of the fin 32. However, the thermal deformation member 40 may be provided on the surface of the tube 31 in the heat exchanging portion of the exterior heat exchanger 13. That is, the plural thermal deformation members 40 may be arranged separately in dispersion in the entire range of a surface of the heat exchanging portion of the exterior heat exchanger 13 adapted as an evaporator in the heating operation mode.

(4) In the above-described embodiments, the plural thermal deformation members 40 are arranged separately in dispersion in the entire range of the surface of the heat exchanging portion (e.g., fin 32 or/and tube 31). However, the plural thermal deformation members 40 may be arranged continuously at least in some area or all area of the surface of the heat exchanging portion (e.g., fin 32 or/and tube 31), without dispersion. Even in this case, the thermal deformation members 40 may be arranged to cover all the surface area of the heat exchanging portion, or may be arranged to cover a part of the surface area of the heat exchanging portion. When the thermal deformation members 40 are arranged in a wide area on the surface of the heat exchanging portion of the exterior heat exchanger 13, the ice attached to the surface of the heat exchanging portion of the exterior heat exchanger 13 can be effectively removed.

(5) In the above-described first embodiment, the thermal deformation member 40 is configured by the two-kind shape memory alloy; however, may be configured by one-kind shape memory alloy. For example, in the above-described first embodiment, the first member 41 may be provided in the material deformation member 40 while an elastic member is used instead of the second member 42. Alternatively, the second member 42 may be provided in the material deformation member 40, while an elastic member is used instead of the first member 41.

Alternatively, the fin 32 may be used instead of the second member 42 without additionally proving the second member 42 in the material deformation member 40. In this case, by using the elasticity of the fin 32, the fin 32 may be expanded in the normal operation. When the temperature of the fin 32 made of the second member 42 is increased more than the transformation temperature of the first member 41, the first member 41 is constricted.

(6) In the above-described first embodiment, the rotation speed of the compressor 11 of the first operation in the defrosting operation is set based on the detected temperature of the refrigerant temperature sensor. However, the rotation speed of the compressor 11 of the first operation in the defrosting operation may be set based on the relationship between the refrigerant temperature and the rotation speed of the compressor 11, so that the refrigerant temperature flowing to the exterior heat exchanger 13 becomes the second temperature T2.

In the above-described first embodiment, the rotation speed of the compressor 11 of the second operation in the defrosting operation is set at the target rotation speed in the normal operation of the heating operation mode. However, the rotation speed of the compressor 11 of the second operation in the defrosting operation may be set at a rotation speed other than the target rotation speed in the normal operation of the heating operation mode, if the rotation speed of the compressor 11 can be set higher than that in the first operation and the refrigerant temperature flowing into the exterior heat exchanger 13 can be made lower than the material deformation temperature Tc.

The refrigerant discharge capacity of the compressor 11 may be suitably controlled, if the refrigerant temperature of the exterior heat exchanger 13 is changed between the first temperature T1 that is lower than the material deformation temperature and the second temperature T2 that is higher than the material deformation temperature.

(7) In the above-described embodiments, a fixed-displacement type compression mechanism is used as the compressor 11, and the rotation speed of the electrical motor of the compressor 11 is controlled by the controller 16 so as to control the refrigerant discharge capacity of the compressor 11. However, a variable-displacement type compression mechanism may be used as the compressor 11 to control refrigerant discharge amount by controlling the refrigerant discharge capacity of the compressor 11.

(8) In the above-described first embodiment, in the defrosting operation, the first operation is set in the compressor 11 so that the refrigerant discharge capacity of the compressor 11 is reduced and the refrigerant temperature flowing into the exterior heat exchanger 13 is increased. However, the second operation as the normal operation of the compressor 11 in the heating operation mode may be maintained in the defrosting operation, while a part of high temperature refrigerant higher than the refrigerant temperature flowing into the exterior heat exchanger 13 is introduced into the exterior heat exchanger 13. Even in this case, the temperature of the exterior heat exchanger 13 can be increased in the defrosting operation.

The exterior heat exchanger 13 of the above-described embodiments and modifications thereof may be suitably used for a refrigerant cycle device shown in FIG. 11. FIG. 11 is a schematic diagram showing a refrigerant cycle device 1 that is a modification example of FIG. 1 described in the above first embodiment. In a refrigerant cycle 10 shown in FIG. 11; a bypass passage 17 and a switching valve 18 for opening or closing the bypass passage 17 are provided, with respect to the refrigerant cycle 10 shown in FIG. 1. The bypass passage 17 is provided such that a part of the refrigerant before being drawn into a refrigerant suction side of the compressor 11 returns to a refrigerant inlet side of the exterior heat exchanger 13 in the defrosting operation. Furthermore, a check valve 19 is provided in the bypass passage 17 so that refrigerant flows in one way through the bypass passage 17. The controller 16 causes the switching valve 18 to be closed in the normal operation, and causes the switching valve 18 to be repeatedly opened and closed in the defrosting operation, during the heating operation mode.

When the exterior heat exchanger 13 is operated as an evaporator, the temperature of the refrigerant after performing heat exchange in the exterior heat exchanger 13 is higher than the temperature of the refrigerant flowing into the exterior heat exchanger 13. Thus, by repeatedly opening and closing of the switching valve 18, the refrigerant temperature can be changed in the exterior heat exchanger 13.

The refrigerant cycle 10 may be configured such that as part of the refrigerant discharged from the compressor 11 flows into the exterior heat exchanger 13, in the defrosting operation of the exterior heat exchanger 13.

(9) Furthermore, the refrigerant temperature flowing into the exterior heat exchanger 13 may be increased by using any means or method that is generally known. For example, the refrigerant cycle 10 may be switched to the cooling operation mode when the defrosting operation of the exterior heat exchanger 13 is performed. Alternatively, a hot gas cycle may be provided in the refrigerant cycle 10 so that hot gas refrigerant discharged from the compressor 10 is directly introduced into the exterior heat exchanger 13 when the defrosting operation of the exterior heat exchanger 13 is performed.

Alternatively, the surface temperature of the heat exchanging portion of the exterior heat exchanger 13 used as an evaporator may be changed by using a heater such as an electrical heater or the like, without using the control of the refrigerant temperature.

Even in this case, the temperature increase and the temperature decrease of the surface temperature of the heat exchanging portion of the exterior heat exchanger 13 are repeatedly performed, so that the thermal deformation member 40 is deformed in the defrosting operation.

Even in this case, in the defrosting operation, the temperature of the exterior heat exchanger 13 can be controlled to be increased to a temperature lower than the freezing point, and it is unnecessary to increase the temperature of the exterior heat exchanger 13 to be higher than the freezing point. Thus, it is possible to reduce the temperature of the exterior heat exchanger 13 for a short time after the temperature of the exterior heat exchanger 13 is increased to a temperature. As a result, the heat energy used in the defrosting operation can be effectively reduced.

(10) In the above-described embodiments and modifications thereof, the refrigerant cycle 10 with the exterior heat exchanger 13 is used for a vehicle air conditioner. However, the refrigerant cycle 10 with the exterior heat exchanger 13 may be used for an air conditioner for home use, a water heater using a heat pump cycle, and a freezer of a refrigerator car or the like.

(11) The above described embodiments may be suitably combined if there is no contradiction therebetween.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. A heat exchanger usable as an evaporator in a refrigerant cycle device, the heat exchanger comprising: a heat exchanging portion configured to perform heat exchange between refrigerant and air so as to evaporate the refrigerant; and a thermal deformation member provided in en entire range on a surface of the heat exchanging portion, to be deformed bordering on a predetermined temperature when the surface of the heat exchanging portion is frosted to produce ice, wherein the thermal deformation member is deformed by a temperature change between a first temperature lower than the predetermined temperature and a second temperature higher than the predetermined temperature, to cause distortion between the surface of the heat exchanging portion and the ice when the ice is attached to the surface of the heat exchanging portion.
 2. The heat exchanger according to claim 1, wherein the predetermined temperature is lower than freezing point.
 3. The heat exchanger according to claim 1, wherein the thermal deformation member includes plural thermal deformation parts which are arranged separately in dispersion in the entire range of the surface of the heat exchanging portion.
 4. The heat exchanger according to claim 3, wherein a distance between adjacent thermal deformation parts at an upstream portion of an air flow is larger than a distance between adjacent thermal deformation parts at a downstream portion of the air flow, on the surface of the heat exchanging portion.
 5. The heat exchanger according to claim 1, wherein the thermal deformation member has an angle portion on its outer surface.
 6. The heat exchanger according to claim 1, wherein the thermal deformation member is made of a shape memory alloy.
 7. The heat exchanger according to claim 6, wherein the thermal deformation member includes a first, member having a transformation temperature, and a second member having a transformation temperature lower than that of the first member, when temperature of the thermal deformation member is increased from a temperature lower than the transformation temperature of the first member to a temperature higher than the transformation temperature of the first member, the first member becomes in a memorized shape and the second member is deformed by the memorized shape of the first member, and when the temperature of the thermal deformation member is decreased from a temperature higher than the transformation temperature of the first member to a temperature lower than the transformation temperature, the first member is deformed by elastic force of the second member.
 8. The heat exchanger according to claim 1, wherein the thermal deformation member is made of an organic material or a complex material which is deformable by a temperature change bordering on the predetermined temperature.
 9. The heat exchanger according to claim 1, wherein the thermal deformation member is made of a bimetal.
 10. The heat exchanger according to claim 3, wherein the thermal deformation parts at an upstream portion of an air flow are respectively larger than the thermal deformation parts at a downstream portion of the air flow, on the surface of the heat exchanging portion.
 11. The heat exchanger according to claim 10, wherein the sizes of the thermal deformation parts are gradually reduced from an upstream air side to a downstream air side.
 12. The heat exchanger according to claim 1, wherein the heat exchanging portion includes a plurality of tubes and a plurality of fins which are alternately arranged in an arrangement direction, and the thermal deformation member is provided on at least one of the tubes and the fins.
 13. A refrigerant cycle device comprising: a compressor configured to discharge refrigerant; a refrigerant radiator in which the refrigerant discharged from the compressor radiates heat; a decompression device configured to decompress the refrigerant flowing out of the refrigerant radiator; the heat exchanger according to claim 1, adapted as an evaporator for evaporating the refrigerant flowing out of the decompression device; and a control portion configured to repeatedly change a surface temperature of the heat exchanging portion between a first temperature lower than the predetermined temperature and a second temperature higher than the predetermined temperature.
 14. The refrigerant cycle device according to claim 13, wherein the control portion is configured to repeatedly change the surface temperature by changing a refrigerant discharge capacity of the compressor.
 15. The refrigerant cycle device according to claim 14, wherein the control portion causes the compressor to be switched between a first operation, in which a discharge capacity of the compressor is lower than that of a normal operation, and a second operation in which the discharge capacity of the compressor is higher than the discharge capacity of the compressor in the first operation, when the surface of the heat exchanging portion of the evaporator is frosted in the normal operation.
 16. The refrigerant cycle device according to claim 13, further comprising: a bypass passage through which a part of high-temperature refrigerant higher than the refrigerant flowing into the evaporator is introduced to the evaporator; and a switching portion configured to open or close the bypass passage, wherein the control portion repeats the opening and closing of the switching portion so as to repeatedly change the surface temperature of the heat exchanging portion, when the surface of the heat exchanging portion is frosted.
 17. The refrigerant cycle device according to claim 16, wherein the bypass passage is configured such that a part of the refrigerant after flowing through the evaporator and before flowing into a refrigerant suction side of the compressor is introduced to a refrigerant inlet side of the evaporator. 